Protective helmet



NOV. 21, 1967 A, LA$TN|K ETAL 3,353,187

PROTECTIVE HELMET Filed Nov. 19, 1965 United States Patent Otlice3,353,187 Patented Nov. 21, 1967 3,353,137 PRGTECTIVE HELP/1E1 AbrahamL. Lastniir, Framingharn, Mass, and Meyer 1. Landsberg, St. Louis Park,Mina, assignors to the United States of America as represented by theSecretary of the Army Filed Nov. 19, 1965, Ser. No. 598,875 8 Claims.(Cl. 2-3) This invention relates to a protective helmet and, moreparticularly, to a protective helmet that provides greater impact energydissipating characteristics and greater resistance to penetration byballistic fragments than that heretofore provided by helmets of the samegeneral weight and size.

It has been established that the incidence and severity of head injuriesto personnel involved in hazardous, highspeed activities, as forexample, military aircraft crew'- men, can be significantly reduced bythe use of proper protective helmets. One study indicated that over a 36month period there were 80% fewer fatal head injuries among personnelinvolved in military aircraft accidents who wore protective helmets ascompared with personnel who did not. A helmet furnishes protection tothe head of the wearer by virtue of its ability to dissipate some or allof the energy of an impact delivered to the helmet before that energycan be transmitted to the head. It has been demonstrated that to obtainoptimum protection, the energy of the impact applied locally must firstbe caused to be distributed over as wide an area as possible and thenthe impact energy which has thus been distributed must be required to dosome work before it can be transmitted to the head. It is known in theart that this kind of protection can be obtained by means of a helmethaving a rigid outer shell and a liner of energy absorbing material. Theouter shell should be sufi'iciently rigid so as to resist localizeddeformation in response to the force of an impact. Metal shells, forexample, while rigid, characteristically deform in a small localizedarea in response to an impact. Resin-impregnated, glass fabriclaminates, on the other hand, form hard, tough, shells highly resistantto localized deformation and capable of distributing the energy of theimpact over a wide area of the shell. Glass fabrics were thought to bepreferred for this purpose because of the high tensile strength andstretch resistance of glass fibers. However, because of the difiicultyof obtaining a satisfactory laminar bond, it has been necessary to usefrom 40% to 70% by weight of resin based on the weight of the shell.While such a high resin content is necessary to produce a helmet shellthat has the desired degree of rigidity and resistance to deformation,it also results in a material that affords little protection againstpenetration by ballistic fragments. It is known, on the other hand, thatthese same glass fabrics when bonded With 25% resin produce structureshaving significant resistance to ballistic fragment penetration but asthe resin concentration increases and the structure becomes more rigid,ballistic fragment penetration resistance decreases.

The inner energy absorbing liners employed in crash protective helmetsconsist of nonresilient materials that will undergo an irreversibledeformation when the energy of an impact exceeds a certain level. Energyis llllillZld in crushing or deforming these liner materials and, as aconsequence, this energy never reaches the head. Examples of a goodenergy absorber for use in a crash protective helmet are the expandedplastics which have a rigid cell structure, such as polystyrene andpolyurethane. It is preferred that the expanded plastic material havesufficient strength in compression to resist crushing under low energyimpacts, otherwise a number of butfeting (low energy) blows to the headwould crush the liner destroying its effectiveness as an energyabsorber. The head can normally withstand low energy impacts Withoutinjury when the force of the impact is distributed over a relativelywide area but when the energy of the impact exceeds 50 foot lbs. somemeans must be employed to absorb and extend the time duration duringwhich the head receives the impact energy.

It is therefore among the objects of the present invention to provide animproved crash protective helmet.

Another object is to provide a helmet that has greater energydissipating characteristics than helmets of the prior art.

A further object is to provide a crash protective helmet that will alsoprovide a significantly high resistance to penetration by ballisticfragments.

These and other objects of the present invention will become apparentfrom the following detailed description wherein reference is had to theaccompanying drawings in which:

FIGURE 1 is a front elevation of an embodiment of our crash protectivehelmet.

FIGURE 2 is a sectional view of our helmet taken along the line 22 ofFIGURE 1.

FIGURE 3 is a sectional view through the outer shell of the helmet.

The improved crash protective helmet of the present invention consistsof a hard outer shell and an inner liner of energy absorbing material,wherein the outer shell is composed of a resin-bonded laminate of nyloncloth" in place of the resin-impregnated laminate of glass cloth usedheretofore. The use of nylon cloth to form the outer shell results in atotally unexpected improvement in the crash protective qualities of thehelmet since it would be expected that a resin-bonded nylon cloth shellwould be less rigid than a resin-bonded glass cloth shell, because ofthe lower tensile and stretch-resistant properties of nylon. Reductionin rigidity of the shell would be expected to result in a reduction inthe ability of the shell to distribute and attenuate the load of theimpact.

The outer shell of the helmet of our invention is a resin-bondedlaminate of nylon fabric and, as illustrated in the drawings anddescribed in detail hereinafter by way of example, is constructed ofnine plies of nylon ballistic cloth. This cloth is formed by weaving ahigh tenacity, continuous filament nylon prepared fromhexamethylenediamine and adipic acid or its derivatives and having amelting point of 250i6 C. The warp and filling yarns are 1050 denier,multifilament with 3 to 4 turns per inch Z twist and the weave is 2 by 2basket weave with two ends weaving as one and two picks Weaving as one.The cloth weighing approximately 14 oz. per sq. yard is thoroughlyscoured and heat treated and has a minimum of 46 yarns per inch in thewarp and 42 yarns per inch in the filling and has a minimum breakingstrength in the warp of 900 lbs. and in the filling of 825 pounds, and aminimum ultimate elongation of 25% in the warp and 20% in the filling.Further details relative to this nylon ballistic cloth may be found inMilitary Specification MIL-C-12369D (GL) entitled, Cloth, Ballistic,Nylon. The nine plies of nylon cloth are surface-coated on each sidewith a resin composition, such as a thermosetting resin modified with athermoplastic resin, e.g., a modified system of polyvinyl butyral andphenol-formaldehyde resins. A suitable modified system contains amixture of 87 parts by weight of an ethanol solution of polyvinylbutyral (25% solids), 10 parts by weight of phenolic varnish (57%solids), 27 parts by weight of trimethylol phenol (60% solids) and 2.6parts by weight of phthalic anhydride dissolved in 5 parts by weight ofmethanol. It is essential that the resin composition. be sufficientlyviscous so as to remain on the surface of the fabric and not flow intothe fabric. The resin composition is knife coated onto each side of thefabric to effect an add-on of from 35 to 50% and preferably about 40% byweight of the resulting structure. The exposed surfaces of the laminateare coated with a phenolformaldehyde resin to create a hard, rigidsurface. The coated cloth plies are trimmed so as to form pin-wheel likecutouts when inserted in a mold to form a rough helmet shape. Each plyisinserted in the mold so as to stagger the overlapped areas and so asto avoid gaps. Following the placement of the requisite number of pliesof coated fabric in the mold, a rubber bag is inserted within the cavityand inflated with steam heated water under pressure. The temperature ofthe water is aproximately 330 to 360 F., the pressure within the bag isfrom 300 to 400 p.s.i. and the molding time is aproximately 45 minutes.The mold in which the plies are inserted consists of a split metalcavity which is cored for heating by steam. It is desirable that heat beapplied to .both sides of the shell structure being formed in order toobtain a uniform cure.

The energy absorbing liner is an expanded plastic, molded, for example,from an expandable polystyrene bead material, having a thickness ofapproximately 1 /2- inch, a minimum density of at least 4 lbs. per cubicfoot and a minimum compressive strength of 80 p.s.i., i.e., the abilityto withstand this load without breaking or being compressed more than25% of original thickness. This material is molded in the, general shapeof the helmet and is cemented in place to the inner Wall of the shelleither in one piece, or cut into sections which are assembled in place.

Resilient material, such as expanded latex may be used in the form ofpads to make the helmet more comfortable to wear and as means foradjusting the size and fit of the helmet. Such resilient materials,however, do not contribute to the protection afforded the head sincethey only absorb a small amount of energy when compressed, which energyis returned with the recovery of the material. As a consequence, thehead may be subjected to greater accelerative forces than normallyexpected because of the sudden change in direction as a result of therebound.

Various studies have shown that damage to the head and brain are relatedto the time span during which the force of the impact is transmitted tothe head, and to the maximum accelerative forces transmitted to thehead. Head and brain damage tolerance limits cited in terms of peakacceleration and duration of impact vary among investigators but thereis general agreement to the effect that a helmet, when impacted shouldnot bottom, nor permit an excess of 400 G to be transmitted to the headnor should the duration of transmission of impact forces be less than 4,milliseconds. Bottoming is defined as that phenomenon occurring duringimpact or crushing of energy absorbing systems when input energy istransmitted to the sensing element with little or no attenuation, aswill be reflected by a sudden and rapid rise in the forcetime curve.

The crash protective properties of a helmet can be ascertained,therefore, by subjecting the helmet to the force of an impact andmeasuring the peak accelerative forces transmitted through the helmet,the time span during which these forces are transmitted, and theresistance of the helmet to bottoming. These impact tests are performedon a free swinging, hollow, magnesium alloy head form weighing 13pounds. An accelerometer is mounted to the inner surface of the headform below the point to be impacted and connected to instrumentation torecord acceleration and the time span. of the impact. The helmet beingtested is placed on the head form and is impacted with a 16 pound steelmass with a 1.9 radius impacting surface dropped from a height of 6.25feet above the helmet. The results of two successive impacts on theforehead region of the nylon shell helmet of this invention and theglass shell helmet, both helmets having essentially the same dimensionsand weight, are set forth below in Table I. It is noted thatacceleration is expressed in Gs, i.e., a unit of force applied to a bodyequal to the force exerted on it by gravity.

The results shown above indicate that the nylon helmet transmitssignificantly less accelerative forces to the headform and that theaccelerative forces transmitted are spread over a wider time frame thanin the case of the glass helmet. The second impact delivered to theglass helmet generating forces in excess of 400 G caused bottoming.

The helmet of this invention was evaluated as a barrier which willresist penetration by. ballistic shell fragments and was compared with aglass helmet of essentially the same weight and size. A caliber .22 17grain fragment simulating projectile having a hardness of Rockwell C30-2 was fired on each helmet to produce an impact normal to the line offire. The V i.e., the impact velocity at which there is a 50%probabilityof penetration by the projectile, was determined for eachhelmet type. Replicate tests resulted in an average V of 1,110 feet persecond for the nylon helmet and an average V of 400 feet per second forthe glass helmet.

Referring to the drawing, there is shown an embodiment of a helmet 10according to our invention which is shaped so as to provide a protectivecovering for the head of a wearer. The principal components of thehelmet are a rigid outer shell 11 and an inner liner 12 of energyabsorbing material cemented in place against the inner surface of theshell. There is also shown a visor housing 13 constructed of the samematerial as the shell 11 which serves to enclose a transparent visor 14.A visor lock assembly 15 holds the visor in position within the visorhousing and when released from its locked position allows the visor tobe moved into position in front of the face. A chin strap 16 mounted onthe front of the helmet and a nape strap 17 on the rear of the helmetfunction 'to hold the helmet to the head of the wearer. An enlargedfragmentary view in section of the resin-bonded plies of nylon fabric isshown in FIGURE 3 with the plies of fabric identified as 20, themodified resin composition layer as 21 and the phenol-formaldehydelayers as 22. V

The invention described in detail in the foregoing specification issusceptible to changes and modifications as may occur to persons skilledin the art without departing from the principle and spirit thereof. Theterminology used is for purpose of description and not limitation, the

scope of the invention being defined in the claims.

We claim:

1. A crash and ballistic protective helmet comprising a rigid outershell formed of a plurality of plies of a Woven nylon fabric, said pliesbonded togetherby a resin where said resin comprises at least 35% byweight based on the weight of the. shell, an inner energy absorbingliner of, irreversibly crushable expanded plastic material and meansattaching said inner energy absorbing liner to the inner surface of saidrigid outer shell.

2. A crash and ballistic protective helmet according to claim 1 whereinsaid resin is a thermosetting resin modified with a thermoplastic resin.

3. A crash and ballistic helmet according to claim 2 in which said wovennylon fabric is a 2 x 2 basket weave fabric, weighing about 14 02.,having a minimum of 42 yarns per inch in the filling and warp.

4. A crash and ballistic helmet according to claim 3 in which said nylonfabric has a minimum breaking strength of 900 pounds in the warp and 825pounds in the filling and a minimum ultimate elongation of in the warpand 20% in the filling.

5. A crash and ballistic helmet according to claim 3 wherein said resinis a modified system of polyvinyl butyral phenol-formaldehyde resins andwhere said resin comprises from to by weight based on the weight of theshell.

6. A crash and ballistic helmet according to claim 5 wherein said innerenergy absorbing liner has a density of at least 4.0 lbs. per cubic ft.and a minimum com pressive strength of p.s.i.

7. A crash and ballistic helmet according to claim 6 wherein said innerenergy absorbing liner is an expanded polystyrene bead material having athickness of not less than about /2-inch.

8. A crash and ballistic helmet according to claim 7 wherein said outershell is constructed of nine plies of nylon fabric.

References Cited UNITED STATES PATENTS 2,351,235 6/1944 Shroyer et al.2-6 2,879,513 3/ 1959 Hornickel et al. 23 2,971,195 2/1961 Voss 2-33,018,210 1/1962 Frieder et al. 23 XR 3,237,202 3/1966 Aileo 26 JORDANFRANKLIN, Primary Examiner. I. R. BOLER, Assistant Examiner.

1. A CRASH AND BALLISTIC PROTECTIVE HELMET COMPRISING A RIGID OUTERSHELL FORMED OF A PLURALITY OF PLIES OF A WOVEN NYLON FABRIC, SAID PLIESBONDED TOGETHER BY A RESIN WHERE SAID RESIN COMPRISES AT LEAST 35% BYWEIGHT BASED ON THE WEIGHT OF THE SHELL, AN INNER ENERGY ABSORBING LINEROF IRREVERSIBLY CRUSHABLE EXPANDED PLASTIC MATERIAL AND MEANS ATTACHINGSAID INNER ENERGY ABSORBING LINER TO THE INNER SURFACE OF SAID RIGIDOUTER SHELL.